Before you run a Hazel rule, though, you would be wise to run a dry run by clicking the preview button (image 1). Even better, when in preview mode, you can check why the rule caught or missed files by clicking the info button (Image 2) next to the file or folder. This is very handy to verify complex Hazel rules with Subfolder Depth or Sub-file/folder Count as conditions.
[thanks Gerard!]